Novel poling method for piezoelectric 0-3 composites and transfer to series production

Integration of piezoceramic particles into polymers is considered to meet current and future challenges of function integration in lightweight engineering. Especially composites with integrated piezoceramic transducers for sensory tasks such as condition or structural health monitoring are gaining importance. A possible, mass production compatible manufacturing approach is the direct formation of a piezoceramic particle-electrode-assembly during the processing by integrating the ceramic and its electrodes into the polymer matrix. The piezoelectric particles are then fully surrounded by the polymer matrix, forming a so-called 0-3 composite (Newnham et al., 1978). However, it is unpoled and inactive and thus requires poling to activate the piezoelectric properties. It is known that poling of piezoelectric particles in a polymer matrix is difficult due to the misfit in dielectric constants of polymer and ceramic. To overcome this obstacle, a poling process that is conducted during the uncured stage of the polymer matrix is introduced in the present paper, making use of the relatively low electrical resistance of the selected polymer in the uncured state. In a first step, the method is modelled and experimentally verified using specimen made of PZT pearls embedded in epoxy resin. In these preliminary experiments, effective piezoelectric charge coefficients up to 28.6 pC/N were achieved. The method is transferred and integrated into the production of fibre-reinforced polyurethane composites. Effective piezoelectric charge coefficients of 5.5 pC/N are obtained for the polyurethane based composites.